1. Field of the Invention
The present invention relates to an optical encoder and a reference signal generation method for the optical encoder.
2. Description of Related Art
Optical encoders that detect a position of a detection head with respect to a scale are widely used to detect a position of a measurement device and the like. A scale of an incremental encoder is provided with a displacement detection pattern for detecting a relative position of the detection head with respect to the scale, and a reference point detection pattern for detecting a reference position. The incremental encoder is capable of converting relative position information detected from the displacement detection pattern into absolute position information based on the reference position detected from the reference point detection pattern. Therefore, it is required that the incremental encoder detect a reference position with high accuracy.
Japanese Patent No. 3358854 discloses an optical rotary encoder having a configuration in which a first light-receiving element and a second light-receiving element are arranged in parallel in a movement direction of a scale. As shown in FIG. 21, the rotary encoder disclosed in Japanese Patent No. 3358854 generates a reference signal based on a first output signal V11 output from the first light-receiving element, a second output signal V12 output from the second light-receiving element, a third output signal V13 generated by reducing the amplitude of the first output signal V11, and a fourth output signal V14 generated by reducing the amplitude of the second output signal V12.
In the rotary encoder disclosed in Japanese Patent No. 3358854, a cross-point between the second output signal V12 and the third output signal V13 is used as a starting point of the reference signal and a cross-point between the first output signal V11 and the fourth output signal V14 is used as an end point of the reference signal. The width and timing of the generated reference signal can be adjusted by adjusting an amplification factor when the first output signal V11 and the second output signal V12 are input to a signal processing circuit.